1. Field of the Invention
The present invention relates to a wired board with bump electrodes and a method of fabricating the same, and, more particularly, to a bump electrode and a method of fabricating the same.
2. Description of the Related Art
There is a fabrication method for a wired board with bump electrodes which is discussed below.
FIGS. 1A to 1E are schematic cross-sectional views showing a conventional fabrication method of a wired board with bump electrodes.
As shown in FIG. 1A, a minute pit 11 with a pyramid shape is formed on a silicon (Si) substrate 10 by anisotropic etching.
Next, a metal film 12 is formed on the Si substrate 10 and a resist 13 is plated and formed on the metal film 12, then the plated resist 13 is opened at the upper portion of the pit 11, as shown in FIG. 1B.
Then, an Au layer 14 to be an electrode is buried in the opening in the plated resist 13 by plating, as shown in FIG. 1C.
Next, an Sn-plated copper lead 15 is aligned with the pit 11 and the Au layer 14, and an Sn plating 16 applied to the copper lead 15 is contacted to the Au layer 14 and is bonded to the Au layer 14 by thermo-compression bonding, thus yielding an Au—Sn alloy between the Sn plating 16 and the Au layer 14 as shown in FIG. 1D.
As the Sn-plated copper lead 15 is separated from the Si substrate 10 thereafter, the Au layer 14 formed on the Si substrate 10 is transferred to the Sn-plated copper lead 15, forming an Au protruding electrode on the Sn plating 16.
In this case, a high-concentration diffusion layer may be used in place of the metal film 12 (see Japanese Patent Laid-Open No. 48445/1983).
However, the prior art has a shortcoming such that it the metal film 12 is formed on the Si substrate 10, the Au layer 14 is not transferred to the Sn-plated copper lead 15 efficiently because of a high adhesion strength between the metal film 12 at the pit 11 and the Au layer 14.
On the other hand, the formation of a high-concentration diffusion layer in place of the metal film 12 requires thermal diffusion or ion injection to the Si substrate 10 over a long period of time, and thus takes time. This makes it difficult to mass-produce products, which may lead to a cost-up of the products.
Further, as the adhesion strength between the high-concentration diffusion layer of the Si substrate 10 at the pit 11 and the Au layer 14 is low, the Au layer 14 may be separated from the Si substrate 10 by external force, such as shocks, applied at the time of, for example, transporting or washing the Au-formed Si substrate, thus lowering the yield.